Do you ever get the urge to try random obscure operating systems? I think it's sometimes just fun to use systems that are not widely used. What obscure operating systems have you tried (or have thought about trying)? I've been looking into
Haiku
[1] lately.

[1] http://en.wikipedia.org/wiki/Haiku%5F%28operating%5Fsystem%29

Why the downvote? I've seen many similarly styled questions here on superuser. Some of them have become quite popular. This question doesn't seem to contradict the standards in the FAQ. It is certainly not subjective; it simply asks other superusers what obscure systems they have looked into. - DLH

sometimes people like to downvote because they are bored. - Stefano Borini

ReactOS® is a free, modern operating system based on the design of Windows® XP/2003. Written completely from scratch, it aims to follow the Windows® architecture designed by Microsoft from the hardware level right through to the application level. This is not a Linux based system, and shares none of the unix architecture.

The main goal of the ReactOS project is to provide an operating system which is binary compatible with Windows. This will allow your Windows applications and drivers to run as they would on your Windows system. Additionally, the look and feel of the Windows operating system is used, such that people accustomed to the familiar user interface of Windows® would find using ReactOS straightforward. The ultimate goal of ReactOS is to allow you to remove Windows® and install ReactOS without the end user noticing the change.

It was based on the design of NT4 when I first heard of it :)
Mind you, WINE was trying to clone the APIs of Windows 3.1 when I first heard of that. - U62

(1)
It is/will be good for compatibility with old software. It is impossible for anybody to compete with MS when talking about new MS systems. - liori

(1)
When it's done it'll be absolutely amazing. As of right now, it has a tendency to be more unstable than Windows 95. - JamesGecko

Very promising project, but yeah, right now stability is an issue. Most times it boots for me, but uptime is measure in minutes typically. If I had time, I'd love to join the project. - Brian Knoblauch

This would be great for running in a virtual machine... Couple it with VirtualBox and you've got a great way to run Windows apps that WINE pukes on. - redwall_hp

MenuetOS is an Operating System in development for the PC written entirely in 32/64 bit assembly language, and released under the
License
[2]. It supports 32/64 bit x86 assembly programming for smaller, faster and less resource hungry applications.

Menuet has no roots within UNIX or the POSIX standards, nor is it based on any operating system. The design goal has been to remove the extra layers between different parts of an OS, which normally complicate programming and create bugs.

Menuet's application structure is not specifically reserved for asm programming since the header can be produced with practically any other language. However, the overall application programming design is intended for easy 32/64 bit asm programming. Menuet's responsive GUI is easy to handle with assembly language.

I wouldn't normaly suggest any windows product for something like this. But, there is enough people now that have never seen nor touched windows 3.1 or earlier. It is a good wakeup call on how far we have come in the windows world.

(1)
@grawity They have no WPA support either. You should be asking who the hell uses an encrypted network?, to which the response is Everybody. - new123456

5

[+9]
[2009-08-12 20:38:15]
bill weaver

OS/2
[1] - Great OS for its time. I believe OS/2 is destined to be the most important operating system, and possibly program, of all time. As the successor to DOS, which has over 10,000,000 systems in use, it creates incredible opportunities for everyone involved with PCs. -- Bill Gates

[1] http://en.wikipedia.org/wiki/OS/2

(2)
Absolutely a superior design to Windows at the time. Took Windows years to catch up with OS/2! - Brian Knoblauch

(1)
+1 as i was actively involved in the developement of OS/2 Warp, good to see it still around as eCommStation ... or as the funny folks over at L'Inq put it two years ago: OS/2 is 20 years old - dead but still walking :) theinquirer.net/inquirer/news/1005311/os-dead-walking - community_owned

6

[+8]
[2009-08-12 20:15:20]
Scott Dorman

Geos
[1] (GeoWorks). Used by the very first versions of America Online when they changed to a graphical interface. It was a full GUI that fit on a single 3.5" floppy with room for both the OS and an application.

[1] http://en.wikipedia.org/wiki/GeoWorks

I used to use this at School. Awesome tetris game :p - EvilChookie

It was also used on early versions of the Nokia Communicator cellphone before they switched to Symbian. - U62

Great OS, made by the same people that originally made Unix. It's and a research project and not that modern anymore. It's taken the unix philosophy to the next level and it's a bit sad unix didn't adopt these philosopies , aldthough a few have crept in.

[1] http://plan9.bell-labs.com/plan9/

I heard it was From Outer Space? - MT_Head

@MT_Head, Bell Labs is an organization secretly run by extraterrestrials (people from the viscinity of Betelgeuse). So, yes. - new123456

NeXTSTEP shipped for 5 different arch (NeXT hardware (68k), SPARC, PARISC, x86 (damn, forget 5), and was in some stage of development for at least 3 (88k, Hobit, Alpha) more, an you could run app in NT (was that number 5?) and I think Solaris. It is the direct ancestor of OS X.

OS/2 was the thing, 15 years ago.

Beos was nifty, but missed it's shot. It took all of 7 seconds to go from finishing hardware boot on a dual Pentium Pro to ready for you to log into the GUI.

DexOS, is a free and open source
32-bit games console type operating
system for 32-bit x86 computers. It
was written entirely in assembly
language using FASM (flat assembler).
The operating system's GUI was
inspired by modern video game consoles
but it also includes a command line
interface. It was designed to boot
from a 1.44 MB floppy disk and its
kernel is less than 100KB. DexOS can
also be booted from a CD, USB flash
drive or hard drive.

[1] http://www.dex4u.com/

(1)
I wonder if it's possible to port interactive fiction runtimes for use with this. I'm not essentially a programmer :) but I hope it's possible given DexOS's theme. Thanks for mentioning this. - Isxek

@Isxek I'm definitely going to try something like that this summer, if I have enough time! - AndrejaKo

A small, open source, educational OS used in a lot of Computer Science OS courses

[1] http://www.cs.washington.edu/homes/tom/nachos/

++ This has by far the best name here. - new123456

17

[+4]
[2009-08-12 22:11:30]
Joakim Elofsson

AROS
[1] Research Operating System, AmigaOS clone for x86. It's based on Amiga OS 3.1 APIs.
The A in AROS was originally Amiga.

[1] http://aros.sourceforge.net/

18

[+3]
[2009-08-12 20:04:50]
juanjux

CP/M on my old Amstrad CPC664 (you used a boot disk), it was not unkown but certainly it was obscure.

We also had CPM on the Commodore 128 - Jim C

(4)
CP/M was hardly obscure - it was the standard business operating system before PCs and MSDOS took over. - U62

19

[+2]
[2009-10-13 07:17:04]
Snark

QNX
[1] was funny to play with at a time. It's a very small and light real-time OS mostly used for embedded systems, although it runs (ran?) on PCs.

They had a demo version booting from a floppy disk (1.44 Mb!), complete with TCP/IP, a graphical interface and a web browser.

[1] http://www.qnx.com/

20

[+2]
[2009-08-12 22:28:45]
John Fouhy

I remember running (I think) Caldera OpenDOS as a replacement for MS-DOS. A DOS with mutli-tasking!

That was before we moved to Windows 3.1, then OS/2 Warp..

(1)
I did DOS multi-tasking with IBM's Topview, then later on Quarterdeck's DESQview. - Brian Knoblauch

21

[+1]
[2009-09-06 03:38:02]
kloucks

The OASIS ("Online Application System Interactive Software") Operating system written by Phase One Systems was a multitasking OS that ran on a 4mhz Z80 chip. RM-COBOL and BASIC and z80 assembler were the development tools

22

[+1]
[2010-02-24 17:29:49]
Peter M

The original and best
OS-9
[1] by Microware. Not the Apple OS of the similar name. In the late '80's I was running OS-9 on a Tandy color computer with 512k of memory, on a 6809. This OS had genuine pre-emptive multi tasking. It is a great system for embedded work.

[1] http://www.microware.com/Products/Microware/OS-9-RTOS.html

23

[+1]
[2009-08-12 22:28:26]
U62

VSTa
[1]. Microkernels were quite the thing in the '90s and VSTa was a research operating system that had a decent following but never quite achieved the following of other open-source unix-alikes.

[1] http://www.vsta.org:8080/

24

[+1]
[2009-08-13 10:37:21]
LKM

Oberon
[1] is awesome. I've written about it
here
[2]. It's a text-based graphical zoomable operating system, and in addition to booting with it, you can run it as an application inside other operating systems.

I will suggest DEC's
TOPS-20
[1] (aka TWENEX), popular from about 1975 to 1985. It reminds a bit about OpenVMS. The shell's user interface is interesting in particular, with immediate command help and guiding words.